In a computer system, various data items are retained in storage apparatuses connected to servers. If a server fails, access to data in a storage apparatus connected to the failed server is often disabled. Thus, there may be a case in which a data access environment for storage apparatuses is deteriorated.
In view of the above situation, to enable access to data in a storage apparatus even if a server to which the storage apparatus is connected fails, identical data is redundantly retained in storage apparatuses connected to a plurality of servers. Thus, even if a server fails, data identical to data managed by the failed server is acquired from another server, enabling service to be continued. An example of technologies by which data is made redundant in server units is the Redundant Array of Independent Nodes (RAIN).
An example of technologies by which data is made redundant is a mirroring technology. In the mirroring technology, a copy (redundant data) of data in a hard disk drive (HDD) managed by a server is stored in an HDD managed by another server (mirror server). Another technology by which data is made redundant is so-called replication. In replication, a replica of data managed by a server is managed by another server so that the original data and the replica are synchronized with each other. In replication, it is possible to manage replicas created in data units called objects in a plurality of servers in a distributed manner.
If data is made redundant as described above, then even if one server fails, service may be continued. If a server fails, however, data redundancy is lowered and data reliability is also lowered. Thus, recovery processing is carried out to recover redundancy. In recovery processing, a copy of redundant data of data that has been managed by the failed server is transferred to a normal server, for example. After this, the server that has received the copy of the redundant data manages the received data.
One technology that is applied when a failure is found in an active server is a technology in which a network connection between the active server and another server used as an alternate is changed.
Japanese Laid-open Patent Publication No. 2007-164394 discloses a related technique.
In recovery processing in which data is recovered by being transferred, however, it takes time in recovery. That is, the more data is recovered is, the more time is spent in recovery. Particularly, since services in which cloud computing is used have recently become widespread, the amount of data managed by a single server has become large. Accordingly, much more time is taken to recover from a server failure. When time taken for recovery processing is prolonged, a time period during which the redundancy of data is low is also prolonged, lowering reliability.